The present invention relates to a surgical device for dilating an opening formed in a bodily tissue structure. More particularly, it relates to a hand-held instrument configured to provide controlled dilation of an opening in a bodily tissue structure, such as an anulus of a spinal disc.
The vertebral spine is the axis of the skeleton upon which all of the body parts xe2x80x9changxe2x80x9d. In humans, the normal spine has seven cervical, twelve thoracic and five lumbar segments. The lumbar segments sit upon a sacrum, which then attaches to a pelvis, in turn supported by hip and leg bones. The bony vertebral bodies of the spine are separated by intervertebral discs, which act as joints, but allow known degrees of flexion, extension, lateral bending and axial rotation.
The typical vertebra has a thick interior bone mass called the vertebral body, and a neural (vertebral) arch that arises from a posterior surface of the vertebral body. Each narrow arch combines with the posterior surface of the vertebral body and encloses a vertebral foramen. The vertebral foramina of adjacent vertebrae are aligned to form a vertebral canal, through which the spinal sac, cord and nerve rootlets pass. The portion of the neural arch that extends posteriorly and acts to protect a posterior side of the spinal cord is known as the lamina. Projecting from the posterior region of the neural arch is a spinous process. The central portions of adjacent vertebrae are separated and supported by an intervertebral disc.
The intervertebral disc primarily serves as a mechanical cushion between the vertebral bones, permitting controlled motions within vertebral segments of the axial skeleton. The normal disc is a unique, mixed structure, comprised of three component tissues: The nucleus pulposus (xe2x80x9cnucleusxe2x80x9d), the anulus fibrosus (xe2x80x9canulusxe2x80x9d), and two opposing vertebral end plates. The two vertebral end plates are each composed of thin cartilage overlying a thin layer of hard, cortical bone which attaches to the spongy, richly vascular, cancellous bone of the vertebral body. The end plates thus serve to attach adjacent vertebrae to the disc. In other words, a transitional zone is created by the end plates between the malleable disc and the bony vertebrae.
The anulus of the disc is a tough, outer fibrous ring that binds together adjacent vertebrae. This fibrous portion, which is much like a laminated automobile tire, is generally about 10 to 15 millimeters in height and about 15 to 20 millimeters in thickness. The fibers of the anulus consist of 15 to 20 overlapping multiple plies, and are inserted into the superior and inferior vertebral bodies at roughly a 30 degree angle in both directions. This configuration particularly resists torsion, as about half of the angulated fibers will tighten when the vertebrae rotate in either direction, relative to each other. The laminated plies are less firmly attached to each other.
Immersed within the anulus, positioned much like the liquid core of a golf ball, is the nucleus. The anulus and opposing end plates maintain a relative position of the nucleus in what can be defined as a nucleus cavity. The healthy nucleus is largely a gel-like substance having a high water content, and similar to air in a tire, serves to keep the anulus tight yet flexible. The nucleus-gel moves slightly within the anulus when force is exerted on the adjacent vertebrae with bending, lifting, etc.
The spinal disc may be displaced or damaged due to trauma or a disease process. A disc herniation occurs when the anulus fibers are weakened or torn and the inner tissue of the nucleus becomes permanently bulged, distended, or extruded out of its normal, internal anular confines. The mass of a herniated or xe2x80x9cslippedxe2x80x9d nucleus can compress a spinal nerve, resulting in leg pain, loss of muscle control, or even paralysis. Alternatively, with discal degeneration, the nucleus loses its water binding ability and deflates, as though the air had been let out of a tire. Subsequently, the height of the nucleus decreases, causing the anulus to buckle in areas where the laminated plies are loosely bonded. As these overlapping laminated plies of the anulus begin to buckle and separate, either circumferential or radial anular tears may occur, which may contribute to persistent and disabling back pain. Adjacent, ancillary spinal facet joints will also be forced into an overriding position, which may create additional back pain.
Whenever the nucleus tissue is herniated or removed by surgery, the disc space will narrow and may lose much of its normal stability. In many cases, to alleviate pain from degenerated or herniated discs, the nucleus is removed and the two adjacent vertebrae surgically fused together. While this treatment alleviates the pain, all discal motion is lost in the fused segment. Ultimately, this procedure places greater stress on the discs adjacent the fused segment as they compensate for the lack of motion, perhaps leading to premature degeneration of those adjacent discs. A more desirable solution entails replacing in part or as a whole the damaged nucleus with a suitable prosthesis having the ability to complement the normal height and motion of the disc while stimulating the natural disc physiology.
The first prostheses embodied a wide variety of ideas, such as ball bearings, springs, metal spikes and other perceived aids. These prosthetic discs were designed to replace the entire intervertebral disc space and were large and rigid. Beyond the questionable efficacy of these devices is the inherent difficulties encountered during implantation. Due to their size and inflexibility, these first generation devices require an anterior implantation approach as the barriers presented by the lamina and, more importantly, the spinal cord and nerve rootlets during posterior implantation, could not be avoided. Recently, smaller and more flexible prosthetic nucleus devices have been developed. With the reduction in prosthesis size, the ability to work around the spinal cord and nerve rootlets during posterior implantation has become possible.
Generally speaking, these reduced size prostheses are intended to serve as a replacement for the natural nucleus. In other words, the anulus and end plates remain intact, and the prosthesis is implanted within the nucleus cavity. Assuming that anulus integrity has not been overly compromised and that internal, lateral forces are minimized, the anulus will subsequently heal, resulting in a near-normal disc function. To this end, a number of different prosthetic nucleus designs have been developed. A common concern associated with these designs is minimizing stress placed on the anulus during implantation. In order to implant a prosthesis within the nucleus cavity, an appropriately sized passageway must be provided through the anulus. Obviously, reducing the overall size of the passageway minimizes resulting anulus trauma. With this in mind, two general design techniques have been identified for reducing the requisite anulus opening size. First, the prosthesis may be configured to increase from a relatively small size prior to implant, to a larger size following implant. With this approach, the reduced, pre-implant size of the prosthesis minimizes the requisite passageway size. Alternatively, the prosthesis may include several independent, relatively small portions, each of which are implanted through a correspondingly small passageway in the anulus. It should be understood that so long as it is minimized, xe2x80x9ctraumaxe2x80x9d resulting from formation of the passageway is in no way permanent. Instead, the anulus tissue will regenerate, repairing the passageway.
While the particular prosthetic nucleus design selected has a distinct affect on resulting anulus damage, an equally important constraint is actual formation of the opening or passageway through the anulus. One technique entails complete removal of a plug of tissue from the anulus via an incision created by a scalpel, punch or similar tool. Entire removal of an anulus segment is highly traumatic, and limits the ability of the anulus to properly heal. Attempts to reattach the anulus plug have been unavailing in that properly orientating and securing of the anulus plug with a suture has proven difficult at best. Alternatively, a flap can be Imparted into the anulus tissue. This technique overcomes the reattachment problems associated with the anulus plug approach. Unfortunately, however, the thickness of the anulus requires formation of a relatively large flap, therefore increasing anulus trauma. Further, it may be difficult to retain the flap in a retracted position throughout the implantation procedure. A third, more viable procedure is to dilate a small opening or incision in the anulus to a size sufficient for prosthesis implantation. The overlapping, plied nature of the anulus tissue renders the anulus highly amenable to incision dilation.
An additional advantage presented by the above-referenced anulus incision dilation approach relates to the fact that in many circumstances, the anulus hag a preexisting opening through which the nucleus originally herniated. Thus, it may be unnecessary to initially impart an opening through the anulus. Alternatively, or in addition, a small incision can be made through the anulus. Regardless of how the opening is formed, subsequent dilation of the opening to a desired size typically requires the use of at least three different dilating tools. Each of the tools includes a tapered distal end of a fixed size configured to expand or dilate the opening upon insertion therein. Through successive use of increasingly larger tools, the anulus opening can be dilated to a desired size. While this technique has been successful, certain potential drawbacks have been identified. The requirement of three or more tools greatly increases the time required by a surgeon to complete the implantation procedure, and likewise increases the opportunity for error. Further, each insertion of an instrument into the anulus increases the likelihood of friction, trauma and impaction of tissue. As a result, the time required for the anulus to properly heal is likely increased, and may in fact be prevented from occurring.
Degenerated, painfully disabling intraspinal discs are a major economic and social problem for patients, their families, employers and the public at large. Any significant means to correct these conditions without further destruction or fusion of the disc may therefore serve an important role. To this end, prosthetic nucleus devices have shown great promise. As part of the implantation of such a device, however, current techniques and tools employed to create an anulus opening have not been perfected. Similar concerns exist for other bodily tissue structures, such as the knee, shoulder, etc. Therefore, a need exists for a singular device configured to adequately dilate an opening formed in a bodily tissue structure, such as an anulus.
One aspect of the present invention provides an adjustable surgical dilator for dilating an opening formed in a bodily tissue structure. The surgical device includes an outer tube and an inner rod. The outer tube includes a proximal section, a distal section and a central lumen. The distal section extends from the proximal section and terminates in a distal end. Further, the distal section includes first and second arms each defining an inner surface and an outer surface. The arms combine to form a head tapering in diameter to the distal end. The head is configured to contact bodily tissue and has a variable cross-sectional outer dimension as defined by the outer surfaces of the arms. In one preferred embodiment, the cross-sectional width of the head is variable. The inner rod is co-axially disposed within the central lumen of the outer tube. The inner rod includes a proximal portion and a distal portion. The distal portion extends from the proximal portion and forms a bearing surface for selectively engaging the inner surfaces of the first and second arms of the outer tube, respectively. With this selective engagement, the bearing surface controls the variable cross-sectional outer dimension of the head. Upon final assembly, the inner rod is axially movable relative to the outer tube to dictate a position of the bearing surface relative to the arms.
Prior to use, the inner rod is maneuvered relative to the outer tube such that the bearing surface does not engage the inner surfaces of the first and second arms. At this orientation, the head is relaxed or contracted, assuming a minimum cross-sectional outer dimension. The surgical device is then directed toward the bodily tissue structure in question, for example an anulus of a spinal disc. More particularly, the surgical device is positioned such that the head is placed within an opening formed in the bodily tissue structure such that the head contacts the bodily tissue. The inner rod is then co-axially maneuvered relative to the outer tube such that the bearing surface engages the first and second arms. Further axial movement of the inner rod, and thus of the bearing surface, causes the first and second arms, and in particular the head, to deflect radially. In other words, the variable cross-sectional outer dimension of the head increases or expands with further axial movement of the inner rod. Expansion of the head in turn dilates the tissue opening. Thus, by controlling the position of the inner rod relative to the outer tube, a surgeon dictates a final, dilated opening size. Further, the surgical device affords a surgeon the ability to control the rate at which dilation occurs.
Another aspect of the present invention relates to an adjustable surgical dilator for dilating an opening formed in a bodily tissue structure, such as an anulus of a spinal disc. The surgical device includes an outer tube and an inner rod. The outer tube includes a proximal section, a distal section and a central lumen. The distal section extends from the proximal section and terminates in a distal end. Further, the distal section includes a head and an axial slot. The head tapers in diameter distally to the distal end and is configured for contacting bodily tissue. The axial slot extends from the distal end to a point proximal the head. With this configuration, a variable outer cross-sectional dimension, preferably the width, of the head varies with radial expansion of the axial slot. Finally, the central lumen extends from the proximal section to the axial slot. The inner rod is co-axially disposed within the central lumen and includes a proximal portion and a distal portion. The distal portion extends from the proximal portion and forms a bearing surface for selectively engaging the distal section of the outer tube. the selective engagement controls radial expansion of the axial slot. With this configuration, the inner rod is axially movable relative to the outer tube for providing selective positioning of the bearing surface relative to the distal section of the outer tube.
During use, the inner rod is positioned so as to minimize radial expansion of the slot. With this orientation, the variable outer cross-sectional dimension of the head is as small as possible. The surgical device is then directed toward a bodily tissue structure such that the head is inserted into the opening in the tissue structure. The inner rod is axially maneuvered such that the bearing surface engages the distal section of the outer tube. Engagement of the bearing surface with the distal section causes radial expansion of the axial slot and thus an increase in the variable outer cross-sectional dimension of the head. Because the head is in contact with the tissue structure, this increase in cross-sectional diameter causes the opening to dilate. Further axial movement of the inner rod allows a surgeon to dilate the opening to a desired size.
Yet another aspect of the present invention relates to a method of dilating an opening in a bodily tissue structure such as an anulus of a human disc. The method A includes providing a surgical device including an outer tube and an inner rod. The outer tube co-axially receives the inner rod and forms a radially expandable head at a distal portion thereof. Further, the inner rod is axially movable relative to the outer shaft and includes a bearing surface for selectively expanding the head between a contracted position and an expanded position. The inner rod is maneuvered relative to the outer tube to orientate the head in the contracted position. The head is then inserted within the opening. Finally, the inner rod is maneuvered relative to the outer tube to orientate the head in the expanded position, thereby dilating the opening.